In digital conferencing, a variety of different formats are used for data transmission. Some formats are designed in accordance with international standards, whereas others are designed to comply with particular application specifications for use in specialized markets as agreed to by groups of manufacturers that are suppliers to those markets. For example, Intel Corporation has conferred with other computer equipment manufacturers to develop a Personal Conferencing Specification (PCS) that is an especially useful format for systems connecting personal computers for audio/video conferencing and is becoming a manufacturer's "standard." PCS is intended to be used on the Integrated Services Digital Network (ISDN). The ISDN is also used by equipment that is designed to comply with the international standard of the International Telephony Union (ITU). This ITU standard is formally referred to as the "H.320 standard" which is composed of three major sections: (1) the audio standard (G.728); (2) the video standard (H.261); and the audio/video connection standard for an ISDN connection (H.221).
The PCS and H.320 standards are not compatible. Equipment designed specifically for rise with PCS will not communicate with equipment designed specifically for use with H.320. It is expected that eventually equipment will become available that will operate in accordance with either mode. It is further expected that the preferred mode will be PCS.
FIG. 1 shows a matrix of possible equipment configurations and the expected choices (within the boxes) for the various combinations of equipment at two remote stations. As depicted, whenever the capabilities of both stations' equipment allow for it, the choice mode is to run in the PCS mode. In order to accomplish this it is necessary for the equipment at each station to communicate its capabilities to the equipment at the other station. Applicant has developed a novel technique called "iTONE" for allowing digital transmitting equipment to present itself in a "friendly way" to both PCS and H.320 terminals over the ISDN.
As is well-known to those skilled in the art, the H.320 format uses a "framing" technique for transmission of data. A typical frame contains eighty octets of bits, including an initial frame alignment sequence (FAS) and a bit allocation sequence (BAS). The PCS format, on the other hand, employs a well-known protocol picked many years ago from the IBM SDLC (Synchronous Data Link Control) which uses an HDLC (Highlevel Data Link Control) "flag" to indicate the starting and stopping of a message. These two formats are not normally compatible, but Applicant has discovered an approach which allows a terminal to send out a special identification signal (iTONE) that will identify the terminal and its capabilities equally well to either PCS or H.320 receiving equipment.